Half cycle detector for electronic controls



Dec. 20, 1949 E. c. HARTWIG 2,491,975

HALF CYCLE DETECTOR FOR ELECTRONIC CONTROLS 'Filed May 12, 1948 2.5 23 EE 37 1 23 z: 33

WITNESSES: INVENTOR Fc waraC. War/Ivy wyyz g. BY

ATTORNEY Patented Dec. 20, 1949 UNITED STATES PATENT OFFICE HALF CYCLE DETECTOR FOR ELECTRONIC CONTROLS Application May 12, 1948, Serial N 0. 26,545

11 Claims. 1

My invention relates to electronic control systems and it has particular relation to protective devices for such system.

Electronic high-current switching devices or contactors have, for several years, been used in welding machines. In one such switching arrangement two ignitrons are provided to conduct alternating current of the two polarities. The ignitor current for each ignitron is conducted from the power source through rectifiers and an ignitor switch to the cathode of the ignitron so that when the switch is closed the ignitor receives current which causes the ignitron to become conductive early in the part of the cycle during which the supply voltage is positive at its anode. Welding machines including this contactor are often operated by inexperienced persons who may fail to detect operational faults when such faults do not render the entire machine in operative.

, If one ignitron of this contactor remains continuously non-conductive, the welder using this control will continue to operate but will make an imperfect weld. At the same time the welding transformer will receive unidirectional pulses. The flux in the welding transformer will build up and tend to saturate the transformer core, causing a reduction in the transformer impedance and a corresponding increase in current. The resulting overload current may severely damage the welder. It is impractical in most operations to set the main power line circuit breakers so that they will prevent such an overload since the circuit breakers might interrupt current in response to transient overloads or power source variations.

It is accordingly an object of my invention to provide a simple means whereby welding current shall be interrupted when either of the ignitrons of an ignition contactor is disabled.

Another object of my invention is to provide a simple and economical protective device to prevent overload in a current consumer supplied through an ignition contactor as a result of the failure of an ignitron.

An ancillary object of my invention is to provide a firing network for an ignitron contactor which shall operate to boost the firing current to a magnitude which will insure operation of the ignitron.

Another ancillary object of my invention is to provide a protective network for an ignition contactor which shall also function as an effective firing network.

In accordance with my invention, firing ourrent for the ignitrons of an ignition contactor is transmitted through one of the windings of the transformer which may be called the secondary. The primary of the transformer is connected directly between the cathodes of the ignitrons; that is, in series with the source and load, through a fuse. When one of the ignitrons remains continuously non-conductive, this control transformer becomes saturated. The impedance of the control transformer is lowered and current through the primary is increased and the fuse blows. The flow of load current is then automatically stopped.

The novel features which I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will be understood from the following description of a specific embodiment when read in connection with the accompanying drawing which is a diagrammatic view illustrating a preferred embodiment of my invention.

As illustrated in the drawing, current is supplied from a source of alternating current 3 through a pair of ignltrons it and "I connected in anti-parallel to the primary 9 of the welding transformer ii. The secondary 53 of the transformer is connected between the electrodes l5 and i! in engagement with material If! to be welded. Each of the ignitrons includes an anode 2|, a mercury pool cathode 23 and an ignitor 25 in contact with the cathode.

Transformer 32 is so connected to the ignitors of the ignitrons 5 and i that the terminal of the secondary 36 connected to the ignitor of ignitron 5 is positive relative to the other terminal when the lower terminal of source 3 is positive .relative to its other terminal.

Each ignitron in effect has two ignition sources. One the main supply 3, the other the secondary 36. When the lower supply line of the source of alternating current 3 is positive with respect to the other supply line, the anode of the first ignitron 5 is positive with respect to its cathode 23. One firing circuit for the first ignitron 5 can be traced from the now positive lower terminal of the current source 3 through a line 2?, the rectifier 2a, the secondary winding 3B of the control transformer 32, a contactor 3|, a rectifier 33, ignitor 25 and cathode 23 of the ignitron '5 and the primary 9 of the Welding transformer l I to the other terminal of the source. The second ignition circuit for the first thyratron may be traced from the positive terminal of the secondary 3d of the control transformer 32 through contactor 3|, rectifier 33, the ignitor 25, cathode 23 of thyratron 5, the fuse 4|, the primary 39 of the control transformer 23, rectifier 29 to the negative terminal of the secondary 3E). Under such circumstances an arc is ignited between the anode 2| and the cathode 23 of ignitron 5 and current flows through this ignitron.

When the upper terminal of the source 3 of alternating current is positive, the anode 2| of the ignitron l is positive with respect to its cathode 23. The first firing circuit of the second ignitron "i may be traced from the upper terminal of the source 3 through the primary 9 of welding transformer rectifier 35, contactor 3|, the secondary winding 3!) of the control transformer 32, rectifier 3i, ignitor 25, the cathode 23 of second ignitron i to the other terminal of the source 3. The second ignition circuit of the second thyratron i may be traced from the now positive terminal of the secondary 33 of the control transformer 32 through rectifier 31, ignitor 25, cathode 23 of ignitron 1, the primary 39, the fuse 4|, rectifier 35 and contactor 3| to the negative terminal of the secondary 3!}. Under such circumstances, an arc is ignited between the anode 2| and the cathode 23 of ignitron and current flows through this ignitron.

The contactor 3| can be controlled by a timing system 43 such as is disclosed in my copending application, Serial No. 16,860, filed March 24, 1948, entitled Timers and assigned to Westinghouse Electric Corporation. The contactor 2| of my said application corresponds to contactor 3| here.

To initiate the welding operation, the contactor 3| is closed, allowing current to fiow through the secondary 3c of the control transformer 32, Voltage induced in the secondary 3B of the control transformer 32 by the primary 39 adds to the voltage across the secondary 30 of the control transformer 32 and helps to force ignitor current through the ignitor circuit. The ignitron with which this circuit is to be used requires that the combined direct and induced current flow in its ignitor before the ignitron becomes conductive.

Inthe event that one of the ignitrons becomes disabled, the current flow through the control transformer 32 will be unbalanced. For example, assume that thyratron 5 becomes non-conductive. The voltage impressed on the primary 39 of the control transformer 32 during one-half period of the supply will be equal to the voltage drop across the second igni-tron 1'; therefore, the cur rent flow will be small during this half period. During the other half period the full line voltage will be impressed across the primary 3-6 of the control transformer 32 and the current flow will be large. Such an unbalanced current flow will quickly lead to saturation of the control transformer 32. Asv the control transformer 32 becomes saturated, its inductance. decreases, thecurrent in the primary 39 in the control transformer 32 increases, and the fuse M. is blown. The ignitor current is then sufficiently decreased to terminate the welding operation.

Although I have shown and described a specific embodiment of my invention, I am fully aware that many modifications thereof are possible. For example, the fuse may be replaced by a circuit breaker or by the actuating coil of a relay which, when activated, will open the circuit through the secondary of the control transformer.

The load supplied by the electronic contactor need not be a welding transformer. For example, the load may be a glass mass to be heated, an electric motor or any other of a large group of loads which require alternating current.

In accordance, also, with the broader aspects of my invention, the transformer 32 may be so connected that it blocks the source voltage during firing.

In view of these examples of practicable modifications of my invention I do not intend to restrict its scope except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. For use in an apparatus having main valves for controlling the fiow of current from a source through a load, and a control electrode in each main valve, the combination comprising a Winding on a saturable core, a fuse, connections between said control electrodes and said winding and said fuse, connections between said winding and said valves so that when one of said valves becomes non-conductive, said winding receives current having a direct current component, and connections between said fuse and said control electrodes so that when said fuse is non-conductive said control electrodes do not provide a firing current and none of said main valves can become conductive.

2. For use in an apparatus having main valves for controlling the flow of current from a source through a load and a control eiectrode' in each main valve, the combination comprising a winding on a saturable core, a current overload interrupter which interrupts current through said current overload interrupter when said current exceeds a predetermined magnitude, connections between said control electrodes to said winding and said current overload interrupter, connections between said winding and said valves so that when one of said valves becomes non-conductive, said winding receives current having a direct current component, and terminals for connecting said current overload interrupter to said control electrodes so that when said current overload interrupter is non-conductive said control elec* trodes do not provide a firing current and noneof saidmain valves can become conductive.

3. For use in an apparatus for controlling the flow of current from a source through a load,-

the combination comprising main valves which conduct current from said source tosaid load, a control electrode in each of said mainvalves to control the conductivity of said main valves, a first winding on a saturable core, a fuse, com nections between said control electrodes and said first winding sothat current flowing through said first winding provides current to said control electrode, a second winding on said saturable core adjacent to said first winding, said first and second windings being so wound and so connected to said power source that when current is flowing from said source, magnetic flux produced by current from said source in said second coil opposes flux produced by current frcr-n said source in said first coi-l, saidm-ainvalves being of such a nature that they will remain non-conductive unless their respective control electrodes are receiving current from both said first and said second windings, and connections betweensaid fuse and said first winding so: that, when said fuse is non-conductive, current. insaid first winding cannot be conducted to any one of said control electrodes, said first winding being connected to said valves so that when any one of said valvesremains non-conductive, said first winding receives current having a direct current component.

4. her use in an apparatus for controlling the fiow of current from a source through a load, the combination comprising main valves which conduct current from said source to said load, a control electrode in each oisaid main valves to control the conductivity of said main valves, a first winding on a saturable core, a circuit breaker, terminals for connecting said control electrodes to said first windings so that current flowing through said first winding provides current to said control electrode, a second winding on said saturable core adjacent to said first winding, said first and second windings being so wound and so connected to said power source that when current is iiowing from said source magnetic flux produced by current from said source in said second coil opposes flux produced by current from said source in said first coil, said main valves being of such a nature that they will remain non-conductive unless their respective control electrodes are receiving current from both said first and said second winding and connections between said circuit breaker and said first winding so that, when said circuit breaker is non-conductive, current in said first winding cannot be conducted to any one of said control electrodes, said first winding being connected to said Valves so that when any one of said valves remains non-conductive, said first winding receives current having a greater magnitude when said current is of one polarity than when said current is of the other polarity.

5. For use in an apparatus for controlling the flow of current from a source through a load, the combination comprising main valves which conduct current from said source to said load, a control electrode in each of said main valves to control the conductivity of said main valves, a first winding on a saturable core, and a fuse, connections between said control electrodes and said first winding such that current flowing through said first winding provides current to said control electrode, a second winding on said saturable core adjacent to said first winding, 8, switch in circuit with said second winding so that the closing of said switch connects said second winding to said control electrodes and said power source, said first and second windings being so wound and so connected to said power source that when current is flowing from said source, magnetic fiux produced by current from said source in said second coil opposes flux pro duced by current from said source in said first coil, said main valves being of such a nature that they will remain non-conductive unless their respective control electrodes are receiving current from both said first and said second winding and connections between said fuse and said first winding such that, when said fuse is nonconductive, current in said first winding cannot be conducted to any one of said control electrodes, said first winding being connected to said valves so that when any one of said valves remains non-conductive, said first winding receives current having a direct current component.

6. For use in an apparatus for controlling the flow of current from a source through a load, a first main valve to conduct current of one polarity to said load, a control electrode in said ,flrst main valve, a second main valve to conduct current of the-other polarity to said load, a first winding on a saturable core, a control electrode in said second main valve, said first winding being connected to the cathode of said first main valve and to the cathode of said second main valve, a second winding on said saturable core, rectifiers in circuit with said second winding, said rectifiers and said coils being connected so that current of one polarity flowing from said power source passes through said second winding to the control electrode of said second main valve, and current of the other polarity passes through'said second winding to the control electrode of said first main valve, rectifiers connected to the oath ode and the control electrode of both of said main valves so that current cannot fiow from said cathode to said control electrode of the same main valve, said windings being so oriented that current flow from said source in one of said windings tends to induce increased voltage across the other winding.

7. For use in an apparatus for controlling the fiow of current from a source through a load, a first main valve connected to conduct current of one polarity to said load, a control electrode in said first main valve, a second main valve corinected to conduct current of the other polarityto said load, a first winding on a saturable core, a control electrode in said second main valve, said firstwinding being connected to a terminal of said first main valve and having its other terminal connected to a terminal of said second main valve, a second winding on said saturable core, rectifiers in circuit with said second winding, said rectifiers and said coils being connected. so that current of one polarity flowing from said power source passes through said second winding to the control electrode of said second main valve, and current of the other polarity passes through said second windin to the control electrode of said first main valve. rectifiers connected to the cathode and the control electrode of both of said main valves so that current can fiow from said cathode to said control electrode only through said second winding, said windings being so oriented that current fiow from said source in one of said Windings tends to induce increased voltage across the other winding. 7

8. For use in an apparatus for controlling the flow of current from a source through a load, a first main valve connected to conduct current of one polarity to said load, a control electrode in said first main valve, a second main valve connected to conduct current of the other polarity to said load, a first winding on a saturable core, a control electrode in said second main valve, said first winding being connected to the negative terminal of said first main valve and having its other terminal connected to the negative terminal of said second main valve, a second winding on said saturable core, rectifiers in circuit with said second winding, said rectifiers and said coils being connected so that current of one polarity flowing from said power source passes through said windings to the control electrode of said second main valve, and current of the other polarity passes through said windings to the control electrode of said first main valve, a switch in circuit with said second winding which controls current flow in said second winding, said windings being so oriented that current flow from said source in one of said windings tends to induce increased voltage across the other winding.

9. For use in an apparatus for controlling the flow or current from a source through a load, a

a a m 1 I first main valve connected to conduct current or one polarity to said load, a control electrode in said first main valve, a second main valve connected to conduct current of the other polarity to said load, a first winding on a saturable core, a control electrode in said second main valve, said first winding being connected to the cathode of said first main valveandhaving its other ter minai connected to the cathode or said second main valve, current overload interrupter which interrupts current through said current overload interrupter when said current exceeds apredetermined magnitude, a second winding on said saturable core, rectifiers in circuit with said secand winding, said rectifiers and said coils being connectedso that current of one polarity flowing from said source passes through said second. winding to the control electrode of said second main valve, and current of the other polarity passes through saidsecond winding to the control electrode of said first main valve.

10. In combination, a first valve having an anode, a cathode and a firing electrode, a second valve having an anode, a cathode and a firin electrode, a first connection between said anode of said first path and said cathode of said second, a second connection between said anode of said second path and said cathode of said first, and a saturabletransformer having its primary connectcd between said first and second cathodes and its secondary between said firing electrodes;

11. In combination, a first valve having an anode, a cathode and a firing electrode, a first asymmetric conductor connected to conduct from said cathode to said firing electrode, a second valve having an anode, a cathode and a firing electrode, a second asymmetric conductor-connected to from said cathode of said second path to said firing electrode of said second path, a first connection between said anode of said first valve and said cathode of said second valve, a second connection between said anode of said second valve and said cathode of said first valve, a saturable transformer having its primary connected between said first and second cathodes andits secondary between said firing electrodes, anda circuit inturruptcr between said primary and said first and second cathodes.

EDWARD C. HARTWIG;

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,690,524 Berthold NOV. 6, 1928 2,242,942 Diamond May 20, 1941' 2,250,202 Mattlsita July 22,1941 2,316,566 Constable et al Apr. 13, I943 

